Spectral Variation and Corresponding Changing Mechanism of Suspended Particulate Material Absorption in Poyang Lake during Flood Periods

Remote sensing accuracy of the dynamic water environment under a changing environment due to climate and anthropogenic impacts should be improved by a deep understanding of the absorption properties pertinent to the water body. Spectral variation of suspended particulate material (SPM) absorption and its changing mechanism during flood periods of Poyang Lake were analyzed in this study. Absorption coefficients were measured and determined by spectrophotometry using the quantitative filter techniques (QFTs) based on field samples from July 12 to September 06, 2017. Two main optical active constituents (OACs) of SPM including nonalgal and phytoplankton algal particulates were quantified and analyzed in detail. The results suggested that, during study periods, Poyang Lake exhibits an overall high level of suspended nonalgal detritus and algal concentration and lower water clarity, showing a strong absorption by total suspended sediments that are closely related with the land-derived nonalgal detritus material which varied significantly with diverse proportions of minerals and organic materials from multiple sources. Due to variations in phytoplankton community pigment composition, concentration, and package effect, there exists a difference between optical absorption capacity on blue (440) and red (675) portions of bands, the former of which had an obvious enhancement due to the increased effect of accessory pigments in suspended phytoplankton particles from July to September. Evidence also presented that the nonlinear dependency of specific phytoplankton particulate absorption on pigment concentration for various trophic statuses in different periods could be unstable due to relative contributions of the package effect and accessory pigments; this could bring uncertainties to the parameterization of optical models and remote sensing algorithms proposed for accurate applications in lake water environment monitoring.